A typical train includes one or more locomotives, a plurality of railcars and several trainlines. The trainlines include both pneumatic and electrical lines most of which run from the lead locomotive to the last railcar in the train. One pneumatic trainline is the brake pipe. The brake pipe consists of a series of individual pipe lengths each of which is secured to the underside of one railcar. Each pipe length is interconnected to another such pipe length via a flexible coupler situated between each railcar. Usually controlled so as to mimic the pressure contained within a storage tank called the equalizing reservoir, the brake pipe is thus one long continuous pipe that runs from the lead locomotive to the last railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the various reservoirs and operate the brake control valves of each railcar in the train.
The pneumatic trainlines on a locomotive, in addition to the brake pipe, include a main reservoir equalizing (MRE) pipe, an independent application and release (IAR) pipe and an actuating pipe, the latter also known as the No. 13 pipe. Within a locomotive consist (i.e., two or more locomotives connected together), the MRE, actuating and IAR pipes of each locomotive connect to the MRE, actuating and IAR pipes of adjacent locomotives. The IAR pipe supplies the compressed air that may be used to control the delivery of pressurized air to, and thus to operate, the brakes of each locomotive in the train.
The brakes of a train, whether on railcars or locomotives, are applied using brake cylinders and associated components. During braking, the brake cylinders convert the pressurized air that they receive to mechanical force. From the brake cylinders this force is transmitted by mechanical linkage to the brake shoes. When the brakes are applied, it is the brake shoes that are ultimately used to slow or stop the rotation of the wheels on every vehicle in the train.
A typical locomotive has a brake control system such as any one of the various EPIC.RTM. Brake Equipment Systems produced by the Westinghouse Air Brake Company (WABCO). These brake control systems generally include a handle unit, a cab control computer, a keyboard, a display, a locomotive interface unit, a brake control computer and a pneumatic operating unit.
Depending on how a particular locomotive may be configured, the handle unit and the cab control computer may occupy physically separate enclosures or be housed within a single enclosure called the cab control unit, as shown in FIGS. 1 and 2A. The handle unit contains the automatic and independent brake handle assemblies, as shown in FIGS. 2B and 3. From the handle unit the cab control computer receives via an interface card the signals indicative of the positions of the brake handles. Based on these inputs, the cab control computer calculates brake control commands representative of how much, or even if, the braking effort of the train should be raised or reduced. Combined with other data and encoded, the cab control computer conveys these commands to the brake control computer.
The keyboard permits a train operator to provide the various parameters necessary to set-up, and otherwise access, the brake control system. The display allows the operation of the brake equipment to be monitored. The locomotive interface unit (LIU) connects electrical power and certain trainlines to the brake equipment and provides various signals to the brake control computer. Based on the inputs it receives and the software that dictates its operation, the brake control computer controls the overall operation of the brakes. The brake control computer achieves such control by controlling the operation of the pneumatic operating unit (POU). It is chiefly the POU that affects the pressures in the pneumatic trainlines and in the various reservoirs so as to control the brakes according to the commands it receives from the brake control computer.
Among the devices comprising the POU are the independent application and release (IAR) control portion, the brake cylinder (BC) control portion and the brake pipe (BP) control portion. These operating portions of the POU are primarily controlled by the brake control computer. The IAR control portion features pneumatic logic circuitry along with solenoid operated valves by which the pressure in both the actuating and IAR pipes can be controlled. The BP control portion uses pneumatic logic circuitry and solenoid operated valves by which the pressure in the equalizing reservoir and brake pipe of the train can be controlled. The BC control portion features pneumatic logic circuitry along with solenoid operated valves by which the pressure in the brake cylinders on the locomotive can be controlled. The BC control portion controls pressure in the locomotive brake cylinders in response to the commands generated by movement of the brake handles or manifested as pressure changes in the brake pipe or IAR pipe.
A pressure switch (PS) portion senses the pressure in the brake pipe and the actuating pipe under both normal and loss of power conditions. Pressure switch 13A, for example, is used while the brake control system is controlled electronically under normal conditions. It closes when the No. 13 pipe is pressurized. Pressure switch 13B, however, is used while the brake control system has suffered a loss of power. Switch 13B is also set to close when the actuating pipe is pressurized.
Through the keyboard, the train operator can select the mode in which the locomotive brake equipment will be operated. In the LEAD CUT-IN mode, the brake control computer permits the locomotive operator to direct control of the train through both the automatic and independent brake handles. This gives the operator control over the brakes of both the locomotive(s) and the railcars. In the LEAD CUT-OUT mode, the brake control computer permits the locomotive operator to direct control only through the independent brake handle. This gives the operator control over the brakes of the locomotive(s) only. In the TRAIL mode, both brake handles are rendered inoperable except for the emergency position. In a locomotive consist, the brake equipment of one locomotive operating in the TRAIL mode is essentially subservient to the brake equipment of another locomotive operating in either of the LEAD modes. The operation of both the BP and IAR control portions is affected by the mode in which the locomotive is operated.
The automatic brake handle is the device that the train operator can manipulate to direct the brake equipment to apply and release the brakes on all of the locomotives and railcars in the train. The level to which the brake equipment reduces or increases pressure in the brake pipe, and thus the amount of braking power exerted by the train brakes, corresponds to the position of the automatic brake handle. The independent brake handle, in contrast, allows the train operator to apply and release the brakes only on the locomotive(s) of the train.
As best shown in FIG. 1, the automatic brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is zero and the brakes are fully applied. When the brakes are applied, reduction of the pressure in the brake pipe is generally controlled from the lead locomotive via the BP control portion. The exact amount by which the pressure is reduced depends into which of the application positions the handle is placed. It is this reduction in pressure that signals the brake control valve(s) on each railcar to supply pressurized air from the appropriate reservoir(s) to the brake cylinders to apply the railcar brakes. The automatic brake handle positions thus include release, minimum service, full service, suppression, continuous service and emergency. Between the minimum and full service positions lies the service zone wherein each incremental movement of the handle toward the full service position causes an incremental reduction in brake pipe pressure.
Also shown in FIG. 1, the independent brake handle can be moved from and in between a release position at one extreme to a full apply position at the other extreme. The range encompassing a point just next to the release position up to and including the full apply position is referred to as the application zone. When the handle is moved to the release position, the brake control computer commands the IAR control portion to vent air from a control reservoir. This prompts the IAR control portion to exhaust air from the IAR pipe. The BC control portion responds pneumatically to this loss in IAR pipe pressure by venting air from the brake cylinders to release the locomotive brakes.
When the independent brake handle is then moved into the application zone, the brake control computer commands the IAR control portion to increase proportionately the pressure in the control reservoir. The exact amount by which the reservoir pressure is increased depends on how far into the application zone the handle is placed. For example, when the handle is placed into its full apply position, the brake control computer commands the IAR control portion to increase the pressure in the control reservoir to a nominal maximum value appropriate to the type of train at issue. The IAR control portion reacts to this increase in control reservoir pressure by raising the pressure in the IAR pipe accordingly. Responding pneumatically to the resulting increase in IAR pipe pressure, the BC control portion directs air from the main reservoir to the brake cylinders to apply the locomotive brakes. The pressure in the IAR pipe and the locomotive brake cylinders thus reduces and increases in proportion to the position of the independent brake handle.
Another position in which the independent brake handle can be moved is the actuation position (also known as the bail off position), as best shown in FIGS. 1 and 2A. When held in the bail off position, the independent brake handle causes two microswitches, known as the actuation (or bail off) switch and loss of power (LOP) bail off switch, to close. The purpose for these switches is described in the ensuing paragraphs.
The independent brake handle assembly in its current design has exhibited less than the desired level of reliability. This is because the actuation and LOP bail off microswitches are disposed on a part of the assembly that moves during operation. Consequently, these two microswitches along with the wiring that connects to them have evidenced a tendency to wear out at a faster than expected rate. The invention described and claimed in this document has been devised to overcome this problem.
The foregoing background information is provided to assist the reader to understand the invention described and claimed below. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.